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Three Different Letters - Solutions

Approach 1: Using zip to Compare Characters​

Description​

This approach uses the zip function to pair characters from the two input strings and then filters the pairs to count the differences. The function first checks if the strings have the same length, and then counts the number of differing characters. If the count is less than or equal to 3, the function returns true.

Implementation​

func hasNoMoreThanThreeDifferentLetters(_ str1: String, _ str2: String) -> Bool {
    guard str1.count == str2.count else { return false }
    
    let differences = zip(str1, str2).filter { $0 != $1 }
    
    return differences.count <= 3
}

Pros​

  • Efficient in terms of time complexity, as it only requires a single pass through the strings.
  • Simple and concise implementation.

Cons​

  • Requires additional memory to store the array of differing characters.

Approach 2: Using Manual Iteration​

Description​

This approach manually iterates through the characters of the two strings, comparing each pair and counting the differences. This method avoids creating additional collections, potentially saving memory.

Implementation​

func hasNoMoreThanThreeDifferentLetters(_ str1: String, _ str2: String) -> Bool {
    guard str1.count == str2.count else { return false }
    
    var differenceCount = 0
    
    for (char1, char2) in zip(str1, str2) {
        if char1 != char2 {
            differenceCount += 1
            if differenceCount > 3 {
                return false
            }
        }
    }
    
    return differenceCount <= 3
}

Pros​

  • More memory efficient as it does not create an intermediate array.
  • Explicitly checks the condition within the loop, potentially exiting early if the difference count exceeds 3.

Cons​

  • Slightly more verbose compared to the zip and filter approach.

Edge Cases​

  • Strings of different lengths: The function immediately returns false if the lengths are different.
  • Identical strings: The function returns true as there are no differences.
  • Strings with exactly three differing characters: The function returns true.

Conclusion​

The approach using zip to compare characters and filter differences is efficient and concise. However, the manual iteration method can be more memory efficient and allows for early termination. Both approaches are valid and choosing between them depends on the specific requirements and constraints of the application. Understanding both methods provides valuable insights into different ways to compare strings and handle character differences.